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    "## a 和 b 是两个整数，如果他们的差能够被另一个整数 n 整除，则称 a、b 对于模 n 同余\n",
    "\n",
    "记作 $a\\equiv b\\,(\\,mod \\: n\\,)$， 记作 a 和 b 关于模 n 同余。\n",
    " $a\\equiv b\\,(\\,mod \\: n\\,)$ 的等价形式是 $n\\, | \\,(\\,a - b \\,)$，例如：\n",
    " \n",
    " $28\\equiv 16\\,(\\,mod\\: 12\\,)$， $28\\equiv 16\\,(\\,mod\\: 4\\,)$， $19\\equiv -5\\,(\\,mod\\: 12\\,)$"
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   "source": [
    "$a\\equiv b\\,(\\,mod \\: n\\,)$ 理解为 $a - b = kn$， k 是任意整数。当 $a\\equiv 0\\,(\\,mod \\: n\\,)$ 时，则 $n\\:|\\:a$"
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    "\n",
    "同余：$a\\equiv b\\,(\\,mod \\: n\\,)$\n",
    "\n",
    "线性同余方程：$ax\\equiv b\\,(\\,mod\\:n\\,)\\,$\n",
    "\n",
    "乘法逆元：$aa^{-1}\\equiv 1\\,(\\,mod\\:n\\,)\\,$"
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